add a character before a line with matching pattern

Question

I have an array that contains

line number 1
line number 2
line number 3
line number 4
line number 5

Then I ask for the user input:

read userInput
echo $userInput

And then I try to match the user input, which is a number to my array

for i in "${!array[@]}";do
if [["${array[$i]}"="$userInput"]]
then
    echo "~"
    echo " $i"
fi
done

But this doesn't work. The desire output is this:

4
line number 1
line number 2
line number 3
~line number 4
line number 5

Can anyone help me please?

Answer 1

The conditional [[ .. ]] needs whitespace around the operators and values, i.e.

[[ "${array[$i]}" = "$userInput" ]]
  instead of 
[["${array[$i]}"="$userInput"]]

(The latter is interpreted as one word, and the shell tries to find a command with that name.)

Also, ${!array[@]} gives you the indexes to the array. I'm not sure if that's what you want, since in the script you print out the index with echo $i, but your sample output seems to contain the string stored in the array. If don't need the indices in particular, you can just use for value in "${array[@]}".

Then, if you want to match a partial pattern, you need to explicitly tell the shell that anything before and after the pattern should be accepted: [[ "$var" = *$pattern* ]] (no quotes around the pattern). (See here)

So, paraphrasing a bit:

A=("abc" "def" "ghi")
pat=e
for val in "${A[@]}"; do 
    [[ "$val" = *$pat* ]] && echo -n "~"
    echo "$val"
done

prints

abc
~def
ghi